The present invention relates to copper alloys containing magnesium and phosphorous and which exhibit electrical conductivity of 90% IACS or higher and significantly higher strength properties.
Historically, copper has been strengthened by alloying with different elements. With very few exceptions, the additions have sacrificed electrical conductivity properties disproportionately while increasing strength properties. Pure copper, which peaks at a tensile strength on the order of 60 ksi, has an electrical conductivity of 100% IACS at this strength. Thus, pure copper has a strength.times.conductivity factor of 6,000 (60.times.100) units. Brasses, one of the oldest of copper alloy families, while capable of acquiring strength as high as 104 ksi, typically incur a large decrease in conductivity. Cartridge brass, the most popular of the brasses, has a strength.times.conductivity factor of under 3,000 units. Other alloys such as bronzes and copper-nickel alloys have strength.times.conductivity factors that are well below that of pure copper.
Alloys with low element additions, that have electrical conductivities around 90% IACS, have the best combination of strength and conductivity. Zirconium coppers, for example, are capable of producing strips with a strength of 70 ksi with a corresponding electrical conductivity of 90% IACS. The strength.times.conductivity factor of these alloys peaks around 6300 units. However, these alloys are very difficult to produce, suffer from very high variations in properties, and do not exhibit good formability.
Alloys containing magnesium and phosphorous are known in the art. U.S. Pat. No. 3,677,745 to Finlay et al., for example, illustrates a copper alloy containing 0.01 to 5.0 weight percent magnesium, 0.002 to 4.25 weight percent phosphorous and the balance copper. This patent also illustrates copper-magnesium-phosphorous alloys having optional additions of silver and/or cadmium in amounts of from 0.02 to 0.2 weight percent and 0.01 to 2.0 weight percent, respectively.
Alloys of the Finlay et al. type are capable of achieving properties as follows:
i) Tensile strength (T.S.) 90 ksi with 70% IACS conductivity (strength x conductivity factor=6,300); PA1 ii) T.S. 55 ksi with 95% IACS conductivity (strength.times.conductivity factor=5,225); and PA1 iii) T.S. 80 ksi with 70% IACS conductivity (strength.times.conductivity factor=5,600).
Alloys such as these represent the best combinations of strength and conductivity, in some cases exceeding that of pure copper. These alloys have good formability; however, their resistance to heat is limited. High conductivity alloys are used in applications where they are exposed to high temperatures for short durations. These alloys while capable of retaining a significant part of their strength at 710.degree. F., lose an unacceptable part of their strength when exposed to temperatures such as 800.degree. F., even for a few minutes.
U.S. Pat. No. 4,605,532 to Knorr et al. illustrates an alloy which consists essentially of from about 0.3 to 1.6% by weight iron, with up to one half of the iron content being replaced by nickel, manganese, cobalt, and mixtures thereof, from about 0.01 to about 0.2% by weight magnesium, from about 0.10 to about 0.40% phosphorous, up to about 0.5% by weight tin or antimony and mixtures thereof, and the balance copper. The Knorr et al. alloys are based on a high phosphorous to magnesium ratio which is at least 1.5:1 and preferably above 2.5:1. The result of this is that whereas all the magnesium in the Knorr et al. alloys is likely to be tied up with phosphorous, other elements like iron and cobalt will be left in solution in large amounts. As a consequence, electrical conductivity will suffer. The Knorr et al. alloys also contain coarse particles having a size ir. the range of 1 to 3 microns. As a result, the Knorr et al. alloys will exhibit poorer ductility, formability, resistance to softening, and lower strength.times.conductivity factors.
U.S. Pat. No. 4, 427,627 to Guerlet et al. relates to a copper alloy essentially comprising 0.10 to 0.50% by weight cobalt, 0.04 to 0.25% by weight phosphorous, and the remainder copper. The cobalt and phosphorous additions are made so that the ratio of cobalt to phosphorous is between 2.5:1 and 5:1, preferably 2.5:1 and 3.5:1. Nickel and/or iron may be substituted for part of the cobalt; however, the nickel and iron may not be present in an amount greater than 0.15% with nickel being present in an amount less than 0.05% by weight and the iron being present in an amount less than 0.10% by weight. The Guerlet et al. alloys may contain one or more of the following additions: from 0.01 to 0.35%, preferably 0.01 to 0.15%, by weight magnesium; from 0.01 to 0.70%, preferably 0.01 to 0.25% by weight cadmium; from 0.01 to 0.35%, preferably 0.01 to 0.15% silver; from 0.01 to 0.70, preferably 0.01 to 0.2% by weight zinc; and from 0.01 to 0.25%, preferably 0.01 to 0.1% by weight tin. The alloys of this patent suffer from the deficiency that the importance of forming magnesium phosphide and/or iron phosphide particles of particular sizes to improve physical properties such as formability, ductility, and resistance to softening while maintaining high strength properties and electrical conductivity is not recognized.
U.S. Pat. No. 4,750,029 to Futatsuka et al. illustrates a copper base lead material for semiconductor devices. The material consists essentially of from about 0.05 to 0.25% by weight tin, from 0.01 to 0.2% by weight silver, from 0.025 to 0.1% by weight phosphorous, from 0.05 to 0.2% magnesium, and the balance copper and inevitable impurities. The P/Mg ratio is within a range from 0.60 to 0.85 so as to form a compound of magnesium and phosphorous or Mg.sub.3 P.sub.2. Alloys of this type are typically marked by a low strength.times.conductivity factor.
Other copper-magnesium-phosphorous alloys are illustrated in Japanese patent document 55-47337 and Japanese patent document 59-20439. The '337 patent document illustrates a copper alloy containing 0.004 to 0.7% phosphorous, 0.01 to 0.1% magnesium, 0.01 to 0.5% chromium, and the balance copper. Alloys of this type exhibit electrical conductivities in the range of 80 to 90% IACS in an annealed condition; however, the strength.times.conductivity factors are less than desirable. The '439 patert document illustrates a copper alloy containing 2 to 5% iron, 0.2 to 1.0% magnesium, 0.3 to 1.0% phosphorous and the balance copper. Alloys of this type enjoy high strength properties and very low electrical conductivities.
Japanese patent document 53-19920 relates to a copper alloy containing 0.004 to 0.04% phosphorous, 0.01 to 02.0% of one or more of magnesium, silicon, manganese, arsenic, and zinc, and the balance copper. While alloys within these ranges enjoy electrical conductivities in the range of 80 to 90% IACS, they suffer from low strength properties.
U.S. Pat. No. 2,171,697 to Hensel et al. relates to a copper-magnesium-silver alloy. The silver is present in an amount from 0.05 to 15%, while the magnesium is present in an amount from 0.05 to 3%. This patent, on its first page, notes that copper-magnesium alloys containing small proportions of beryllium, calcium, zinc, cadmium, indium, boron, aluminum, silicon, titanium, zirconium, tin, lead, thorium, uranium, lithium, phosphorous, vanadium, arsenic, selenium, tellurium, manganese, iron, cobalt, nickel, and chromium, can be improved by the addition of silver in the aforesaid range. Certainly, there is no recognition in this patent of the need to form magnesium phosphides and/or iron phosphides to provide a very desirable set of physical properties.
Recently, Olin Corporation has issued U.S. Pat. No. 5,868,877. This patent is directed to a copper-iron-magnesium-phosphorous alloy having the same composition as Olin's prior art alloy C197. Olin also has developed certain new alloys, designated 19710 and 19720, which have entered the market place. These alloys contain phosphorous, magnesium, iron, nickel, cobalt and/or manganese, but do not contain any silver. Alloy 19710 contains 0.03 to 0.6 weight % magnesium, 0.07 to 0.15% phosphorous, 0.05 to 0.40% iron. 0.1% max. nickel plus cobalt, 0.05% manganese, and the balance copper. Alloy 19720 contains 0.06 to 0.20% magnesium, 0.05 to 0.15% phosphorous, 0.05 to 0.50% iron, and the balance copper. The alloy designated 19720, per published data, has an electrical conductivity of 80% IACS in soft condition and a tensile strength of 60 to 70 ksi in hard temper.
Despite the existence of these alloys, there remains a need for alloys which demonstrate high electrical conductivity, high strength properties, and excellent ductility, formability, and resistance to softening.